Nested models for convenient grouping and composition
From W3C XForms Group Wiki (Public)
Right now, all the instances, binds, submissions, and actions of a model are aggregated into a single, monolithic asset. There is no language support to allow authors to decompose the model into logical parts.
It would help to be able to compose a model by nesting more models within it.
The instances of nested models could be made visible to containing models.